Thread: connecting 6" (150mm) flexy

Mick, the poly pipe is oversize and the flex might fit inside the pipe.If it's a tad tight, turn a former, angled from 150mm - 155mm. Insert the former into the pipe, heat poly with heat gun and tap the former into the pipe until it stretches enough. Have the sizes on the former, like a step drill.

If the pipe is too big, cut 4 slots 50mm long, a bandsaw kerf is normally enough and squeeze the flex on (cover the slots) and use a pipe clamp to secure.

There are slightly different sized flexies around and I have not found one readily available that fits any PVC junctions neatly.
I have some 6" flexy that is black and green in colour and it does fit neatly inside standard female PVC junctions.
I bought it from a fellow member and have not seen it fore sale anywhere.

Most flexy will fit inside it's corresponding sized female junctions but it will be a loose fit.
If the end of the junction is threaded then a tight hole can be cut in a treaded end cap and forced over the flexy and screwed over the female junction.
For extra sealing and grip, the gap around the flexy is stuffed with thin foam.
This is an expensive solution but give an airtight firm fit with max flow

As Pat says a cheaper solution is to cut lengthwise slits out of a short length of regular ducting - the slits should be just enough so that when the short length of ducting is squeezed together it fits inside the ducting and this will also fit neatly inside the flexy. A hose clamp can them be used to clamp the flexy to the slit ducting and gaffer tape will hold the slit ducting on the regular ducting. This produces a reduced diameter so will slightly reduce the flow.

Another method is to heat a 150 mm section of the middle of a regular piece of ducting and then pull on each end. This produces a tapered reduced radius middle which can be cut in half to make two connections for flexy. Like there previous method this also produces a reduced radius junction.

A better variant of the previous method is one that expands the pipe so the flexy can fit inside it. This can be done with tapered former - heat the end of a pipe in oil and push it over a former. I have a set of expanding plastic jaws for my WW lathe that can hold a 200 mm long piece of 150 mm diameter PVC pipe at one end while a 150 mm diameter wooden live centre holds the other centre red. I set the lathe on it's slowest speed and while it turns and I gently heat the expanding jaw end end with a hot air gun. Every minute or so I stop the lathe and expand the jaws a little. This makes accurate sized openings in regular ducting that can fit regular flexy very neatly. Unfortunately I have no picts of this setup in action but I will see if I can find the bits and dig them out and mock up a photo.

Pat and BobL,

thanks for the suggestions. I am glad to know that it was not just me but am a bit peeved that flexy does not fit more easily. It seems a sad case that it is not made to fit over a standard piece of straight 150mm pipe. Oh well, just another thing that is more complicated than I had expected.

I do not have a heat gun (at least for now) but will try some other methods suggested.

I'd still be interested in how others have attacked this problem

cheers

Mick

Originally Posted by mick59wests

Pat and BobL,

thanks for the suggestions. I am glad to know that it was not just me but am a bit peeved that flexy does not fit more easily. It seems a sad case that it is not made to fit over a standard piece of straight 150mm pipe. Oh well, just another thing that is more complicated than I had expected.

I do not have a heat gun (at least for now) but will try some other methods suggested.

Heating the end of a pipe with hot oil works and pushing the end over a former works equally as well and in some ways better because it's quicker although I think it's a bit messy.

Hi Mick
Unfortunately many of us have had to grapple with the mismatch between PVC and flexi pipe. I am also using Carbatec brand Flexi on John Samuael's advice as it has as a smoother bore and no wire spiral so is easier to stretch. Even so I have had great difficulty getting it over the 160mm OD of PVC.
My solution was to use 150 mm S&D (available in short lenghts at Bunnings) which has a slightly thicker wall thickness. This is only used in short lenghts at the ends of ducts where I want to connect Flexi. I then obtained some 150mm metal ducting joiners at Masters. These are used to join ducting for Range Hoods etc. Fortunately these are just the right size to slide inside both the S&D PVC and the flexi. They have a very thin wall thickness and cause a minimal reduction in pipe Diam. I found that one layer of Insulation tape on the outside of the section that slides inside the PVC end produces a nice airtight joint that can be disconnected easily because no hose clamps are required. There is a slight bulge midway along the joiner which nicely stops the joiner disappearing up the PVc due to the negative pressure in the duct. There is a picture showing the joiner in the PVC in the thread I posted showing the start of my installation.
Cheer
Ron

Originally Posted by ronboult

Hi Mick
Unfortunately many of us have had to grapple with the mismatch between PVC and flexi pipe. I am also using Carbatec brand Flexi on John Samuael's advice as it has as a smoother bore and no wire spiral so is easier to stretch. Even so I have had great difficulty getting it over the 160mm OD of PVC.
My solution was to use 150 mm S&D (available in short lenghts at Bunnings) which has a slightly thicker wall thickness. This is only used in short lenghts at the ends of ducts where I want to connect Flexi. I then obtained some 150mm metal ducting joiners at Masters. These are used to join ducting for Range Hoods etc. Fortunately these are just the right size to slide inside both the S&D PVC and the flexi. They have a very thin wall thickness and cause a minimal reduction in pipe Diam. I found that one layer of Insulation tape on the outside of the section that slides inside the PVC end produces a nice airtight joint that can be disconnected easily because no hose clamps are required. There is a slight bulge midway along the joiner which nicely stops the joiner disappearing up the PVc due to the negative pressure in the duct. There is a picture showing the joiner in the PVC in the thread I posted showing the start of my installation.
Cheer
Ron

Ron,
very much appreciated. I had forgotten about your earlier post (which I just went back and re-read). I have had a few goes at some of the other suggestions but am not very happy with my efforts so far. There is no Masters near me but I will look around (and take the 150mm S&D with me) to make sure the joins are good).
cheers and thanks
Mick

Originally Posted by ronboult

. . . . . . There is a picture showing the joiner in the PVC in the thread I posted showing the start of my installation.

Ron, I had a bit of a look but couldn't find the picture - care to post a link to the picture or specific post it is in?
Thanks

There is a 6"flexi available from Purple Pig that fits quite easily over 6" pvc.

http://www.purplepig.com.au/www/home/

Hi BobL
have reattached photo to this post
Cheers
Ron

Originally Posted by safari

There is a 6"flexi available from Purple Pig that fits quite easily over 6" pvc.

http://www.purplepig.com.au/www/home/

safari,
thanks for the link - for next time. As I already bought 3 metres of it and carried it on 2 trains I am hoping to use it
cheers
Mick

Now, to find a source for the connector mentioned by Ron.....

Try chamfering the end of the pipe with a file mick59wests then use some wax on the pipe. I found that helped to get the flex started on some 4" pipe I had.

If you are using the same flexy I am (Carba Tec - all poly - no wire), heating the end with a heat gun or oil will allow it to expand over a pipe.

The other method I used was to cut a couple of narrow 1 inch deep vees into the end of the flexy and to slide it into a female connector.

have fun!

John

safari and John,

thanks for some further ideas. I am looking at a UK supplier (ebay - fans4less) who have some PVC joiners which I am hoping will do the trick, similarly (is that a word?) to Ron Boult's joiners. I am waiting for them to come back with the actual diameter of their joiners. If they work well, I will post details.

cheers

Mick